The present invention relates to a method and apparatus for effecting beam steering in a traveling wave antenna having low overall profile height or thickness.
Traveling wave antennas are well known and are suited to consumer applications where overall thickness must be kept to an absolute minimum. For example, for automotive applications, it is desirable to install the antenna within a vehicle""s roof region. However, the antenna preferably should not be visible, for aesthetic reasons, and this places a rigid constraint on the overall height of the antenna to about one inch for practicable vehicular applications.
Parallel plate waveguide constructions are disclosed in U.S. Pat. Nos. 5,349,363 and 5,266,961. A scanning antenna suitable for automotive use is disclosed in U.S. Pat. No. 6,014,108.
The waveguides in these patents lack the ability to achieve beam steering in a simple manner. In the known antennas, elevation beam steering is usually effected by rotating the upper plate of the waveguide which contains the radiating apertures. Such antennas are often very large and involve complex mechanical constructions to rotate the plate. Furthermore, they are relatively costly and add significantly to the overall antenna height.
An object of the present invention is to provide apparatus by which beam steering can be achieved in a traveling wave antenna while maintaining a very low overall antenna height.
A further object of the invention is to provide such apparatus in which the wave traveling in the antenna has a planar phase front across the width of the antenna.
A further object of the invention is to provide such apparatus which is simple in construction and can be adapted to a conventional waveguide of a traveling wave antenna.
The wave or beam in the waveguide travels between upper and lower plates and in accordance with the invention, steering of the beam or wave is achieved by providing a second plate guide beneath the lower plate and disposing the feed source in the second plate guide and coupling the energy between the two plate guides through a 180xc2x0 bend main parabolic reflector while simultaneously collimating the phase front by said parabolic reflector. A rotatable subreflector is disposed in the second plate guide and achieves beam steering by changing the angle of incidence of the beam reflected from the subreflector to the parabolic main reflector. The change in angle is effected by pivotally supporting the subreflector and utilizing an actuator to pivot the subreflector about its pivot point. The resulting angular shifting or steering the beam is one dimensional and the steering occurs predominantly in the elevation plane. Azimuth steering is effected by rotating the entire antenna assembly.
A further object of the invention is to provide a method for steering the beam in the waveguide of the antenna, and according to the method, a beam of electromagnetic energy is directed onto the subreflector which reflects the beam to the main reflector which, in turn, reflects the beam to the waveguide of the antenna. The main reflector collimates the beam and provides the linear phase front of the beam in the waveguide. The subreflector is movable to steer the angle of the beam produced by the main reflector.